Guard the Xwayland popup handling with Wayfire's build configuration.
Wayfire only exposes the Xwayland declarations when WF_HAS_XWAYLAND is set.

--- a/copy-capture.cpp
+++ b/copy-capture.cpp
@@ -193,13 +193,16 @@
                 {
                     candidate_root_node->gen_render_instances(instances, [] (auto) {}, view->get_output());
                 }
-            } else if (wlr_xwayland_surface_try_from_wlr_surface(candidate->get_wlr_surface()))
+            }
+#if WF_HAS_XWAYLAND
+            else if (wlr_xwayland_surface_try_from_wlr_surface(candidate->get_wlr_surface()))
             {
                 if (!wf::toplevel_cast(candidate) || (candidate->get_app_id() == view->get_app_id()))
                 {
                     candidate_root_node->gen_render_instances(instances, [] (auto) {}, view->get_output());
                 }
             }
+#endif
         }
 
         for (auto& candidate : wf::get_core().get_all_views())